1. Technical Field
The present invention relates generally to an apparatus and method for obtaining blood samples useful in diagnostic testing, and more particularly, to an apparatus and method for obtaining a non-activated capillary puncture blood sample for blood coagulation assays.
2. Background Art
Blood coagulation is a complex chemical and physical reaction which occurs when blood comes into contact with an activating agent, such as an activating surface or an activating reagent. In accordance with one simplified conceptual view, the whole blood coagulation process can be generally viewed as three activities: agglutination of platelets, blood clotting, and fibrous tissue formation. In vivo, platelets flow through the blood vessels in an inactivated state because the blood vessel lining, the endothelium, prevents activation of platelets. When a blood vessel is damaged, however, the endothelium loses its inert character and platelets are activated by contact with tissue underlying the damaged site. Activation of the platelets causes them to become xe2x80x9cstickyxe2x80x9d and adhere together. Additional platelets then adhere to the activated platelets and also become activated. This process continues until a platelet xe2x80x9cplugxe2x80x9d is formed. This platelet plug then serves as a matrix upon which blood clotting proceeds.
If the chemical balance of the blood is suitable, thrombin is then produced which causes conversion of fibrinogen to fibrin, which forms the major portion of the clot mass. During clotting, additional platelets are activated and trapped in the forming clot, contributing to clot formation. As clotting proceeds, polymerization and cross-linking of fibrin serves as the permanent clot. Thus, platelet activation plays a very important function in blood coagulation. This particular mode of blood coagulation is termed the xe2x80x9cintrinsicxe2x80x9d coagulation pathway.
Blood and plasma also contain a family of serine proteases that regulate the intrinsic clotting process but also regulate the extrinsic coagulation pathway through bypassing a number of early time-consuming steps in the intrinsic coagulation pathway discussed previously. These serine proteases are referred to as coagulation xe2x80x9cfactorsxe2x80x9d, are typically designated with Roman Numerals (with an xe2x80x9caxe2x80x9d suffix added. if the factor is in an enzymatically active state), and operate in a precisely regulated amplification cascade to form blood clots at the site where tissue has been injured. These blood clots act to stop bleeding at the site of injury. This particular mode of blood coagulation is termed the xe2x80x9cextrinsicxe2x80x9d coagulation pathway.
Normal tissue contains a membrane bound glycoprotein, called tissue factor, which is liberated when the tissue is injured. The extrinsic coagulation process begins when this tissue factor forms a complex with coagulation factor VII and/or VII(a). This tissue factor factor VII(a) complex in turn activates factor X, which in concert with co-factor V, transforms the inactive prothrombin protease into the active thrombin enzyme. Thrombin then transforms fibrinogen into fibrin, which forms the actual blood clot.
Blood coagulation tests may be performed for a variety of purposes, including determination of the bleeding susceptibility of patients undergoing surgery and monitoring of patients undergoing anti-coagulation therapy for the prevention of blood clots. A variety of coagulation tests are presently in use. One of the most popular is the xe2x80x9cprothrombin timexe2x80x9d (PT) test which relies on induction of the extrinsic coagulation pathway by activation of coagulation protease factor VII by thromboplastin in a blood sample to be tested.
There have been a variety of devices developed for collecting blood samples. For example, Summers discloses a two-chamber syringe which separates blood cells from plasma. The first chamber is filled with a filtering material which may incorporate anticoagulants. Blood being drawn into the syringe is filtered through this first chamber allowing only the cell-free component of the blood to enter and be collected in the second chamber. See patent No. GB 2,232,599. A second technique for collecting a blood sample is disclosed by Mitchen in his U.S. Pat. No. 5,014,718. The Mitchen reference discloses an apparatus for piercing a patients skin and collecting the resultant blood sample in a liquid vehicle which is adsorbed on to a porous test disk. Mitchen further teaches the addition of an anticoagulant to the liquid vehicle to avoid coagulation and hemolysis.
The above patents by Summers and Mitchen each disclose methods for collecting blood samples. The aim of the Summers patent, however, is to carry out the separation of blood cells from plasma or serum and to thus collect the serum, while Mitchen""s goal is to more efficiently transport blood to a filter paper by increasing the total liquid volume present.
While capillary puncture blood samples may be obtained by puncturing the skin with a lancet or needle, the trauma of such needle injection typically releases tissue juices and the like into the emerging blood thereby modifying the blood coagulation characteristics. Consequently, to achieve optimal test results, freshly drawn venous blood is typically utilized in the PT test. Thus, the PT test is generally limited to clinical laboratories. Although such centralized testing may be adequate for surgical patients, visiting a doctor""s office or a clinic on a regular basis to monitor anti-coagulation therapy is less acceptable. Thus the need for a convenient, practical, and reliable means of obtaining non-activated capillary puncture blood samples at a patient""s home is needed.
Accordingly, it is an object of the present invention to provide a method for obtaining a non-activated capillary puncture blood sample.
A further object of the present invention is to reduce the trauma resulting from tissue puncture by a medical device, such as, a lancet or needle.
Additional objects, advantages, and novel features of the invention shall be set forth in part in the description that follows, and in part will become apparent to those skilled in the art upon examination of the following or may be learned by the practice of the invention. The objects and the advantages may be realized and attained by means of the instrumentalities and in combinations particularly pointed out in the appended claims.
To achieve the foregoing and other objects and in accordance with the purposes of the present invention, as embodied and broadly described herein, the apparatus of this invention may comprise a piercing instrument for obtaining a non-activated capillary puncture blood sample wherein a composition that inhibits contact activation of blood emerging from damaged tissue is removably disposed on the piercing instrument.
To further achieve the foregoing and other objects and in accordance with the purposes of the present invention, as embodied and broadly described herein, the method of this invention may comprise the steps of coating a surface of a piercing instrument with a removable composition that inhibits contact activation of blood emerging from damaged tissue; and puncturing a bodily tissue with said piercing instrument thereby dislodging said removable composition in the puncture.